On production runs of a chip, slight process variations may introduce changes that, over time and/or with other circumstances, cause the circuitry on the chip to not meet their specifications. Such changes may include, but are not limited to, chemical and composition differences, chip physical differences, photo-lithographic differences, pressure and temperature differences, etc. Each of these differences may be slight, but they may accumulate in such a way as to bring the circuitry out of specification.
One approach to recovering out-of-specification chips is to trim components on the chip. Often a parameter, e.g., a voltage, current, a resistance, or a frequency, is measured on the chip in question, and, if the measurement does not meet the specification, a trim is applied to components in the circuit so that that parameter meets its specification. The trim often applies to series arrangement of resistors with metallic connections or fuses shorting out some of the components. The fuses are selectively cut to change the resulting resistance. For example, a VCO (voltage controlled oscillator) may have an RC (resistor/capacitor) delay that determines the frequency of the VCO. The resistance may be trimmed to have the VCO meet its frequency specification.